I would also add (being friends with some self-described socialists) that solidarity is a traditional socialist value. "It's easy to offer an "opportunity" that in practice goes to a few; the hard and serious task is to ensure the means of flourishing to all."

The folks who created Drinking Liberally summarized liberalism (in the U.S. sense of center-left) as follows: "It is better to live for others than only for yourself." I liked that because I think that's probably the best, most succinct statement of a core liberal value; and it's so stated that it could either be the ideal that drives someone's life, or the opposite of the ideal that drives someone's life.